1. Field of the Invention
The present invention relates to heterocyclic compounds having calcium-sensing receptor (CaSR, hereinafter simply referred to as Ca receptor) modulating (agonistic or antagonistic) activity, pharmaceutical compositions containing them and intermediate compounds useful for synthesizing them.
2. Background Art
Calcium ion (hereinafter simply referred to as Ca) plays an essential role to maintain and modulate functions of various cells such as endocrine and exocrine cells, etc., in addition to nerve and muscle. For this reason, the blood Ca level is strictly maintained in a narrow range. Parathyroid hormone (PTH) plays a central role in maintaining this blood Ca level. Therefore, secretion of PTH from parathyroid gland responds sharply to change in the blood Ca level and is must be modulated according to this. In fact, when the blood Ca level is changed, the blood PTH level is rapidly changed in response to this. The possibility of a mechanism by which the extracellular Ca concentration is sensed by parathyroid gland cells and the information transmitted into cells has been pointed out early by Brown et al. In 1993, they succeeded in the cloning and characterization of a Ca-sensing receptor (CaSR; hereinafter, simply referred to as Ca receptor) from bovine parathyroid (Nature, 366, 575-580(1993)).
The Ca receptor is composed of a large terminal extracellular region spanning 600 amino acids at the N-terminal, having seven transmembrane spanning domains like other G protein coupled receptors, and an intracellular region consisting of 200 or less amino acids at the caboxyl C-terminal.
It is considered that, when the extracellular Ca concentration is increased, phospholipase (PL)-C is activated, leading to increase in the intracellular Ca concentration and inhibition of PTH secretion due to increase in inositol triphosphate (IP3). Since when a high value of the extracellular Ca concentration is maintained, the intracellular Ca concentration is thereafter increased continuously, it is considered that influx of Ca from the outside of a cell is also promoted. PL-A2 and D are activated due to increase in extracellular Ca, but there is a possibility that these are via protein kinase (PK)-C and the like which are activated at the same time via Ca receptor. The Ca receptor also inhibits adenylyl cyclase via Gi protein or via arachidonic acid production due to activation of PL-A2 and decreases intracellular cyclic AMP (Bone, 20, 303-309 (1997)).
Ca receptor mRNA is expressed in many tissues, and the expression amount is high, in parathyroid gland, thyroid gland C cell, medulla and cortex thick ascending limb (MTAL and CTAL) of kidney uriniferous tubule, intramedullary collecting tubule (IMCD) and encephalic subfornical organ (SFO) and hippocampus (Bone, 20, 303-309 (1997)). In addition, expression is recognized in many tissues such as encephalic hypothalamus, cerebellum and olfactory nucleus, regions other than TAL of renal uriniferous tubule, lung, stomach, pancreas, intestine and skin. Since the Ca receptor is present in various tissues, its physiological function has yet to be fully understood. However, it is expected that the Ca receptor modulating (agonistic or antagonistic) drug would provide for a novel treatment of various disease states which include the following:
1. Drugs for Treating Bone Diseases
Since the anabolic activity is manifested by intermittent administration of PTH, Ca receptor modulating drugs which are considered to be able to regulate secretion of PTH are promising as a drug for treating osteoporosis. In addition, Ca receptor modulating drugs which are selectable for thyroid gland C cell may be also effective for treating osteoporosis by stimulation of calcitonin secretion. Whether the same Ca receptor as that of parathyroid gland is present in osteoblast, osteoclast and bone cell or not is disputable. However, some Ca-sensing mechanism is assuredly present therein and, therefore, drugs which directly act on them can be expected as a drug for treating bone diseases.
2. Kidney-Acting Drugs
Handling of water and mineral in kidney is not only based on the results of function as a target organ for hormones, such as PTH, vitamin D etc., but also the Ca receptor in kidney is presumed to function in a response to the Ca concentration and the magnesium ion concentration in the extracellular fluid (Kidney Int, 50, 2129-2139 (1996)). Further, it is also considered that Ca receptor modulating drugs may modulate the blood amount in kidney, the amount of glomerulus filtration, renin secretion and activation of vitamin D in addition to control of influx and efflux of water and mineral.
3. Central Nervous System and Endocrine-Acting Drugs
Ca receptor is present in almost all areas in the central nervous system, and is remarkably expressed, in particular, in the hippocampus, cerebellum and subfornical organ (Brain Res, 744. 47-56 (1997)). Although the details of the function are still unclear, the term of Ca receptor expression after birth in the hippocampus is consistent with the term of acquisition of LTP (Long Tightening Phenomenon) (Develop Brain Res, 100, 13-21 (1997)) and, therefore, the relationship with memory and learning can be presumed. Therefore, Ca receptor modulating drugs which are high in brain-blood barrier permeability and selective for the central nerve system may be utilized for treating Alzheimer's disease. In addition, since dry mouth occurs in hypercalcemic patient, Ca receptor modulating drugs may control them. The presence of Ca receptor in mouse pituitary gland cells which secreteACTH has been reported (Mol Endocrinol, 10, 555-565 (1996)). It is also considered that Ca receptor modulating drugs can be applied to Sheehann's syndrome and hypopituitarism or hyperpituitarism.
4. Digestive System-Acting Drugs
It is considered that a Ca receptor is present in the Auerbach nerve plexus of the digestive tract and controls intestinal tract motion. Constipation is known in hypercalcemic patients and stimulation of digestive tract motion is known in hypocalcemic patients in clinical tests. The existence of a Ca receptor in the gastrin secreting cell (G cell) of the stomach has been reported (J. Clin Invest, 99, 2328-2333 (1997)), and intestinal tract absorption, constipation, diarrhea, defecation and secretion of acid in the stomach may be controlled by drugs which act on a Ca receptor in the digestive tract. Further, it has been found that a Ca receptor is present in human colon cancer cell strains and it controls c-myc expression and proliferation (Biochem Biophys Res Commum, 232, 80-83 (1997)), this is better consistent with the fact that the Ca uptake and sideration of colon and rectum cancers exhibit the negative correlation and, therefore, Ca receptor regulating drugs can be expected also as a drug for preventing and treating such cancers.
Various heterocyclic compounds have been disclosed in the prior art. For example, WO 01/53266 discloses a compound of the formula:
where in R, R1 and R2 are independently H, hydroxyl, etc. This compound has a phosphoinositide 3-kinase inhibitory activity and is useful for treating coronary obstruction, etc. Indian J. Chem., Sect. B (1993), 32B(5), 586-9 discloses the synthesis of a compound of the formula:
wherein R is hydrogen, chlorine, methyl or methoxy. However, no utility is disclosed. U.S. Pat. No. 4,746,656 (JP 63-33380 A) discloses a compound of the formula:
wherein R1 is aryl or heterocyclic group, R2 is aryl, etc., R3 and R4 are independently H, alkyl, etc. This compound is a Ca channel blocker.EP 217142 discloses a compound of the formula:
wherein R is hydrogen, alkyl, etc., R1 is hydrogen, nitro, cyano, etc., R2 is phenyl, cycloalkyl, etc., R3 is hydrogen, acyl etc., and R8 is carboxyl, carbamoyl, etc. This compound is also a Ca channel blocker.
However, a heterocyclic compound having Ca receptor modulating activity is not found in the prior art.